The present invention generally relates to methods for production of a hybrid seed product, and more particularly to methods for producing a hybrid seed product while increasing production of hybrid seed of bee-pollinated crops at predetermined hybridity levels, including post production adjustment of percentage of hybridity and verification of percentage of hybridity of the hybrid seed product after harvest.
Hybrid plant varieties offer many desirable agronomic traits. Hybrid plant varieties often provide higher yield than non-hybrid strains. Hybrid plant varieties may also possess higher stress tolerance than non-hybrid varieties, enabling them to survive in less favorable environmental conditions. Furthermore, hybrid plant varieties provide greater efficiency in breeding improvements. Hybridization allows for combination of desirable agronomic traits from different strains.
While hybridization provides these desirable agronomic traits, certain plant species present particular challenges to hybridization. Species such as corn are easily hybridized because the male and female reproductive organs have physical separation. Other species have reproductive parts that are less accessible and have little physical separation between male and female parts. These species are more difficult to hybridize. Bee-pollinated crops, such as alfalfa and soybeans, are examples of species that have male and female reproductive parts that have little physical separation because of the relatively small size of the flower.
Hybrid seed production in these species often employs cytoplasmic male sterile plants, also called female plants. Seed that is produced by female plants from pollinations by pollenizer plants, also called male plants, is mostly hybrid seed. Seed produced from selfing or sibbing by the pollenizer plants is mostly non-hybrid seed. During production of hybrid seed, employing a higher proportion of female plants to pollenizer plants in a hybrid seed production field increases the proportion of hybrid seed to non-hybrid seed. However, current methods for producing hybrid seed result in a significant decrease of seed yield for each individual plant when increasing the proportion of female plants to pollenizer plants. There is therefore a need for methods for increasing the proportion of hybrid seed to non-hybrid seed while maintaining high overall seed yield for a hybrid seed product.
Production of hybrid varieties is subject to federal law requirements that make a high percentage of hybridity very desirable. 7 CFR §201.26 requires that a variety have at least seventy-five percent hybridity to be classified as a hybrid variety. Certain plant species, particularly bee-pollinated species, such as alfalfa and soybeans, present challenges to breeding plant varieties that meet this federally mandated hybridity level. U.S. Pat. No. 3,570,181, herein incorporated by reference, discloses a method for producing hybrid alfalfa using cytoplasmic male sterile alfalfa plants. However, production according to this method results in large reduction of seed yield that makes production of hybrid seed of bee-pollinated crops commercially impractical. U.S. Pat. No. 4,045,912, herein incorporated by reference, discloses a method for producing seed but does not provide for production of seed meeting federal requirements for a hybrid variety. U.S. Pat. No. 4,045,912 is further not concerned with verification of percentage of hybridity at commercial levels of production. Thus, there is a need for methods for production of hybrid seed that provide for high seed yield while maintaining hybridity levels meeting federal requirements.
Production of a certified hybrid alfalfa product requires determination of percentage of hybridity. Determination of percentage of hybridity is often accomplished using methods employing morphological or molecular markers. However, using molecular markers is expensive, takes significant time and is often commercially impractical. In some species, morphological markers require a homozygous recessive gene on one side, and dominance gene on the other side, and are therefore difficult to employ. Furthermore, some plant species present additional difficulties to employing such methods. For example, tetraploid species such as alfalfa have greater complexity in their genetics and inheritance. Another difficulty is the small seed size of some species, such as alfalfa. There is therefore a need for methods for determining or verifying the percentage of hybridity of a particular hybrid that avoid these difficulties.
Separate harvesting of female seed and pollenizer seed is useful for determining percentage of hybridity. Prior methods of separate harvesting for species such as alfalfa require planting female seed and pollenizer seed in separate rows for separate harvesting. However, production of hybrid seed for bee-pollinated crops, such as alfalfa and soybeans, benefits from intermingling to allow a higher percentage of cross-pollination to occur. Planting in separate rows decreases production of hybrid seed, as cross-pollination becomes less frequent due to the distance of the female plants from the pollenizer plants. Where multiple female rows are planted for every male row, such as shown in U.S. Pat. No. 3,570,181, cross-pollination becomes even less frequent. There is therefore a need for methods for separately harvesting female seed and pollenizer seed that allow for intermingling of female and pollenizer plants.
Production of a hybrid seed product is furthermore a long, expensive and labor-intensive process. Prior methods of seed production do not provide for prediction of percentage of hybridity. A method for predicting hybridity levels of seed production of bee-pollinated crops would facilitate production of a hybrid seed product meeting federal standards. This would allow for faster, cost-effective and less labor-intensive production. There is therefore a need for methods for predicting hybridity levels of bee-pollinated crops.
Prior methods of seed production also do not include methods for post-production adjustment of hybridity levels of bee-pollinated crops. A method for adjusting hybridity levels of bee-pollinated crops would also aid meeting hybridity standards for production of hybrid plant varieties. Post-production adjustment of hybridity levels also would allow for production of hybrid plant varieties while employing breeding methods that would not normally result in hybridity levels required by statute. There is therefore a need for post-production methods for adjusting hybridity levels of bee-pollinated crops.
Although hybrid plant varieties are desirable for agronomic reasons, commercial production of many hybrid plant varieties has not been commercially viable, particularly for bee-pollinated crops. The present invention solves these needs and other problems in the field of hybrid seed production by providing, in most preferred aspects, methods for producing a hybrid seed product that includes increasing production of hybrid seed of bee-pollinated crops at predetermined hybridity levels, prediction of percentage of hybridity, determination of percentage of hybridity, post-production adjustment of percentage of hybridity, and verification of percentage of hybridity after harvest.